1. Field of the Invention
The present invention relates to an apparatus and method for performing a plasma process on a target substrate, and particularly to a semiconductor processing apparatus and method of the single substrate type which utilize radio frequency (RF) discharge to generate plasma. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an LCD (Liquid Crystal Display) or FPD (Flat Panel Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In manufacturing semiconductor devices and FPDs (Flat Panel Display), plasma is often used for processes, such as etching, deposition, oxidation, and sputtering, so that process gases can react well at a relatively low temperature. Plasma generation systems used for semiconductor processing apparatuses (plasma processing apparatuses) are classified broadly into the type utilizing glow discharge or RF discharge, and the type utilizing microwaves.
In general, a plasma processing apparatus of the single substrate type utilizing RF discharge includes a process chamber configured to reduce the pressure therein, and a worktable or susceptor disposed in the process chamber and functioning as an electrode as well. A target substrate, such as a semiconductor wafer or a glass substrate, is placed on the susceptor. Then, the pressure within the process chamber is reduced to a predetermined vacuum level, and a process gas is supplied into the process chamber. When the gas pressure within the process chamber comes to a set value, an RF power is applied to the electrode. With this arrangement, the process gas starts electric discharge, thereby generating gas plasma. Using this plasma, a micro fabrication process, such as dry etching, or a film-formation process, such as chemical vapor growth, is performed on a surface or target portion of the substrate.
In such a plasma processing apparatus utilizing RF discharge, as the gas pressure is set low, the density of gas molecules becomes low, thereby making it difficult to start electric discharge (plasma ignition) or sustain the electric discharge. Particularly, where the plasma processing apparatus is of a parallel-plate type, this characteristic is prominent, and, even if the inter-electrode gap is set smaller, or the RF voltage applied across the electrodes is set larger, the energy given to electrons from the electric field, i.e., energy for ionizing gas molecules or atoms, is insufficient, thereby likely making electric discharge unstable. However, as the case may be, plasma processes use a low gas pressure, small inter-electrode gap, or low RF applied voltage, as preferable process conditions. For example, anisotropic etching preferably uses a low gas pressure to obtain a vertically etched shape in a desired state, and thus requires characteristics for starting electric discharge and sustaining the electric discharge within a low pressure range.
As a conventional technique in this field, an ignition plasma method is known, which uses initial conditions to start electric discharge, and then switches them to the main process conditions after the electric discharge has stabilized. Used as the initial conditions suitable for electric discharge are conditions employing a specific high pressure (for example, Jpn. Pat. Appln. KOKAI Publication No. 2003-124198), a different gas, or a high RF power. A method of assisting plasma generation by microwaves or UV rays is also known as being effective.
However, since the ignition plasma method uses conditions different from the main process conditions for a certain period of time, there are some disadvantages in that the process is affected and the throughput is reduced. Similarly, as regards the method employing microwaves or UV rays, there are also some problems in that the process may be affected, and the apparatus becomes complex, which increases the apparatus cost. As a consequence, conventionally, there is no choice but to adopt the type utilizing microwaves, such as ECR (Electron Cyclotron Resonance), in applications for generating plasma under a low pressure.